Proteins

• Proteins are polymers made from amino acids
• Amino acids contain a carboxyl acid group, an amine group and a variable group
• Two amino acids react together to form a dipeptide and a water molecule
• Test for proteins

  • add Biuret reagent
  • mix
  • positive = violet
  • negative = blue
• Primary structure = sequence of amino acids in polypeptide chain
• Secondary structure = how the chain folds into alpha helices and beta pleated sheets
• Tertiary structure = how the chain folds again into 3D shape
• Tertiary structure is held by hydrogen bonds, ionic bonds, disulphide bridges
• Quaternary structure = when more than 1 polypeptide chain are held together
• Hydrogen bonds are weak bonds resulting from electrostatic attraction
• Ionic bonds formed by oppositely charged ions
• Disulphide bridges are strong covalent bonds formed between sulphurs
• Fibrous proteins have structural functions and are long chains with cross bridges
• Globular proteins have functional roles such as enzymes or hormones and are compact spherical shapes
• Protein synthesis is the process where amino acids join to form peptides which then link up to make a protein